1. Field of the Invention
The present invention generally relates to a voltage buffer. More particular, the present invention relates to a voltage buffer and the source driver thereof which are capable of enhancing the slew rate.
2. Description of Related Art
A conventional voltage buffer is usually used to deliver a voltage signal, enhance the driving capability and avoid the output voltage from being affected by a load. The voltage buffer applied in the source driver of an LCD usually comprises an operational amplifier.
FIG. 1 is a schematic circuit drawing of a conventional voltage buffer, wherein the voltage buffer 100 has a negative feedback structure implemented by coupling the output terminal of the operational amplifier 110 to the negative input terminal thereof, while the positive input terminal of the operational amplifier 110 is coupled to an input voltage VINT. In consideration of a virtual short circuit, the output voltage VOUT generated at the output terminal of the operational amplifier 110 is theoretically equal to the input voltage VINT and varies therewith.
The voltage buffer shown in FIG. 1 is applied in the source driver of an LCD. Since the load capacitance of the panel end to be driven by the source driver is quite large, the voltage buffer 100 may fail to quickly regulate the output voltage VOUT to the same level as the input voltage VINT in response to a change of the input voltage VINT. That is to say, the slew rate of the voltage buffer 100 gets lower due to a load.
Along with the increase of the dimension of an LCD, the load capacitance thereof would get larger. If the slew rate of the voltage buffer of a source driver is not effectively improved to adapt the large LCD trend, it is for sure that the LCD display quality will be degraded.